make USE_SCREEN=False imply USE_SYSTEMD=True

In order to start making the transition in the gate make
USE_SCREEN=False also mean USE_SYSTEMD=True. We'll never actually
declare USE_SYSTEMD=True in the gate (as that doesn't exist for stable
branches), but this will let us roll over the existing transition.

We also have to install systemd-python 234 because we are recording
exception info in the journal, and all versions before that had a bug
in processing that.

Remove the somewhat pointless screen following journalctl commands. We
really don't want or need those, and they tend to build up over time.

Depends-On: I24513f5cbac2c34cf0130bf812ff2df6ad76657c

Change-Id: I6af6d1857effaf662a9d72bd394864934eacbe70
diff --git a/files/debs/general b/files/debs/general
index 20490c6..1dde03b 100644
--- a/files/debs/general
+++ b/files/debs/general
@@ -17,6 +17,7 @@
 libmysqlclient-dev  # MySQL-python
 libpq-dev  # psycopg2
 libssl-dev # for pyOpenSSL
+libsystemd-dev # for systemd-python
 libxml2-dev  # lxml
 libxslt1-dev  # lxml
 libyaml-dev
@@ -26,10 +27,8 @@
 pkg-config
 psmisc
 python2.7
-python3-systemd
 python-dev
 python-gdbm # needed for testr
-python-systemd
 screen
 tar
 tcpdump